Phase, frequency and frequency rate are parameters independent of energy of the input signal (i.e., non-energy parameters). There are known methods of estimating signal non-energy parameters based on processing of variables received from a phase-lock loop (PLL).
A method and apparatus are used for estimating changing frequency of a signal received by a satellite receiver, see U.S. Pat. No. 7,222,035. The system includes a PLL having a numerically controlled oscillator (NCO) and a filter of frequency estimates (FFE). The PLL tracks the changing signal frequency and outputs non-smoothed frequency estimates into the FFE. The FFE then smoothes noise in the signal to produce a more accurate smoothed frequency estimate of the input signal.
A system according to K. Sithamparanathan, Digital-PLL Assisted Frequency Estimation with Improved Error Variance, Create-Net Int. Res. Centre, Trento, IEEE Globecom, Nov. 30, 2008-Dec. 4, 2008, includes a PLL having NCO and a moving average filter (MAF) having N-samples length. The frequency estimates are produced by MAF using the frequency information contained in the phase error process of the digital PLL. The precision of frequency estimation by this method is proportional to 1/N.
The apparatus and methods described in U.S. Pat. No. 7,869,554 use a PLL and provide a phase estimation of the input signal from which signal frequency is estimated by a derivative function and low pass filtering.
A DPLL described in U.S. Pat. No. 4,771,250 generates signal phase which is an approximation of the phase of a received signal with a linear estimator. The effect of a complication associated with non-zero transport delays related to the DPLL is then compensated by a predictor. The estimator provides recursive estimates of phase, frequency, and higher order derivatives, while the predictor compensates for transport lag inherent in the loop.
K. De Brabandere et al., Design and Operation of a Phase-Locked Loop with Kalman Estimator-Based Filter for Single-Phase Applications, IEEE 2006, http:**www.esat.kuleuven.be/electa/publications/fulltexts/pub—1620.pdf describes the design procedure of a Phase-Locked Loop (PLL) preceded by a Kalman estimator-based filter. It provides a highly accurate and fast estimate of the 50 Hz electrical grid frequency and phase angle in grid-connected power electronic applications. A Kalman filter is placed before the PLL in order to ensure that the PLL input matches an ideal sinusoidal waveform as closely as possible at all times, even when the voltage is highly distorted by the presence of harmonics. This ensures fast and low-distortion operation of the PLL for single-phase applications.
A method of measuring frequency for sinusoidal signals according to US Patent Publication No. 2011/0050998, published Aug. 31, 2009, entitled Digital Phase Lock Loop Configurable As A Frequency Estimator, provides for obtaining a current signal phase as an argument of a complex number, the in-phase samples being a real part of the number, while the quadrature samples of quadrature signal decomposition components, converted into digital form and filtered, being an imaginary part of the number; receiving and storing a data block from sequential current differences in signal phases; generating a weight function in accordance with the given mathematical equations, which are used to estimate signal frequency.
However, the above methods do not provide optimal frequency measurements when frequency is unstable.
Unlike the methods above, the present invention enables obtaining optimal phase estimates of the input signal and its derivatives at the outputs of a first-type filter or a second-type filter with the help of DPLL variables which are further used to compute NCO full phase and primary phase estimates of the input signal.